1. Field of Invention
The present invention relates to an energy efficient combined refrigerating and air conditioning system utilizing thermal storage. More particularly, the system is especially suited to marine use where small component size and maximum energy efficiency and reliability are desired and where a continuous energy source is often unavailable.
2. Description of the Prior Art
The use of independent refrigerating and air conditioning systems in shipboard applications is common and well established. Most new production vessels come equipped with built-in ice boxes into which a refrigeration evaporator may be installed. Similarly, air conditioners are often installed in a storage locker or engine room and vented through existing walls, bulkheads or cabinets into the cabin area. These refrigerating systems generally use different types of refrigerant gas and operate at different gas pressures than the air conditioning systems. The systems are typically required to operate both concurrently and independently. At sea, energy to power these systems is typically provided by batteries, photovoltaic panels, wind or diesel generators, or auxiliary engines. Energy is usually available only for a limited time and in limited quantity making energy efficiency of primary importance.
Because of these and other unique requirements of marine refrigerating and air conditioning systems it has not previously been practical to combine the systems in such a way as to make common use of major components such as compressors, condensers and cooling pumps. Combining such components would make it possible to reduce the initial cost of the systems and the associated cost of installing them. Also, by using fewer components, less space is taken by the cooling equipment and fewer spare replacement parts need to be carried on long voyages. Using fewer parts also improves the overall system reliability.
Prior art which successfully combines air conditioning and refrigeration is created primarily for use in automobiles where a large and constant supply of energy is provided via an internal combustion engine and variations in the installation requirements are few in number and insignificant. In such applications energy efficiency and installation versatility are second to such considerations as portability, low initial cost and the ability to operate at widely varying compressor speeds. Additionally, because of the short distance between the components, corrections for problems such as liquid line flash gas need not be made. Predictably, these inventions fail to perform satisfactorily when faced with the unique problems of shipboard application.
Means for using a single compressor to supply a plurality of evaporator coils is defined by Muffly, Fujiwara et al (U.S. Pat. No. 4,565,072), Sakano, Fujioka and Tinkey. All require that the compressor and associated equipment be large enough to cool all evaporators simultaneously since no means is provided for the utilization of thermal storage. Without such thermal storage it would be difficult or impossible to maintain stable temperatures during intermittent operation of individual evaporators. Consequently the large capacity which is required increases the size and cost of the system and greatly reduces energy efficiency when only one evaporator (refrigerator or air conditioner) is in use.
In a later patent (U.S. Pat. No. 4,637,222) Fujiwara et al shows a portable refrigerator with thermal storage for use in an air conditioned motor vehicle. This device uses forced air from a second evaporator to simultaneously cool the refrigerated box, it's contents and the thermal storage medium. While solving the thermal storage problem and making intermittent operation possible, such an approach emphasizes portability at the expense of energy efficiency which makes it unsatisfactory for shipboard use. Additionally, such a would suffer from icing of the evaporator if under continuous use as would be the case on a marine vessel.
Sakamoto provides two evaporators and thermal storage, however the device is intended only as an efficient refrigerator/freezer in which both evaporators cool the same space and operate at the same temperature. Altering the device for use as an air conditioner would render it ineffective as a refrigerator.
Tinkey accurately describes some of the problems encountered when trying to eliminate duplicate components in multi-evaporator, multi-temperature systems. However, the invention he describes is meant for simultaneous operation of the various evaporators and would require extensive and costly modification to existing refrigeration compressors.